Double flow jet-engines



p 7, 1965 L. J. BAUGER ETAL 3,204,404

DOUBLE FLOW JET-ENGINES Filed July 30, 1963 United States Patent 4 Claims. (c1. Gil-35.6)

The present invention relates to turbojets of the bypass type in which a cool air stream discharged by the fan or low-pressure compressor of the unit and a hot gas stream issuing from its turbine unite in the jet pipe before exhausting through the nozzle. Such units are sometime provided with an afterburner or reheat device in the jet pipe in order to produce thrust augmentation.

It is desirable that such a device acts on a thermally homogeneous fluid, and to this end it has been proposed to leave a sufiicient length of jet pipe upsteram of the device in order to allow the cool air to intermingle with the hot gas. But this, of course, results in an increase in over-all length and weight of the unit, which is highly undesirable in aeronautics.

It has, therefore, been proposed instead to use a mixer system at the junction of the two streams to unite them into each other. But this solution leads to other drawbacks such as duct losses, complexity of manufacture .and installation of a proper mixer, etc.

The basic object of the present invention is to obtain the desired thermal homogeneity of the mixture in the jet pipe without requiring an extension of the jet pipe nor the presence of a special mixer.

This object is attained primarily by heating the bypass or cool air stream before it joins with the turbine exhaust or hot gas stream. For this purpose, auxiliary burners are provided in the by-pass duct upstream of the plane wherein this duct joins with the turbine exhaust duct.

Now, by-pass turbojets have already been proposed with auxiliary combustion equipment in the bypass duct but for different purposes, viz. for producing thrust augmentation in a manner similar to an after-burner, this auxiliary combustion being considered as a substitute or a complement to ordinary after-burning.

In accordance with the present invention, the by-pass turbojet, which is of the kind having pre-heat burners in the by-pass duct upstream of the above-mentioned plane and re-heat burners in the jet pipe downstream of said plane, comprises temperature responsive means positioned respectively within said ducts just upstream of said plane and designed for generating thermometric signals for controlling the fuel with the detected temperature difference.

The single figure of the accompanying drawing illustrates diagrammatically a twin-spool by-pass turbojet forming an embodiment of the present invention.

This figure shows a multi-stage low-pressure compressor 1 which is preceded by a two-stage fan 2, the assembly being driven by a multi-stage low-pressure turbine 3, whereas a multi-stage high pressure compressor 4 is driven by a single-stage high pressure turbine 5. Between the compressor and turbine sections there is located a combustion chamber 6, which may be annular for example, and which is provided with fuel injectors 7. The gas generator, comprising the central portion of the inlet fan 2, the low and high pressure compressors 1 and 4, the combustion chamber 6 and the low and high pressure turbines 3 and is surrounded by an external casing 9 which provides an air inlet 10 and a nozzle 11 for the by-pass jet-engine. The peripheral portion of the vanes of the inlet fan 2 provides air flow in the annular passage 8 between the gas generator and the external casing 9. e

In this passage 8 there is disposed a pre-heating device 12 having burners, rings or injectors for the feeding of fuel, an ignition device and other related elements.

This pre-heating of the cold flow is controlled in such a way as to bring the cold flow to the same temperature as the hot flow leaving the gas generator, as has been previously mentioned, account being taken of the very short path to be covered by the said flow before it is mixed with that of the gas generator.

Experience shows that equality of the temperatures and pressures is obtained upon leaving the gas generator, so that the normal pre-heating device with its burners and fuel injectors 13, 14 and 15 can be located at this zone, that is to say at the zone where the two flows actually oin.

It will be noted that the intermediate diameter burner ring 14 is intended, more especially, to increase the turbulence at the zone where the two flows join, in such a way as to facilitate the mixture thereof.

The elements 12, 13, 14 and 15 operate only at altitude. On the ground and at full power the elements 16 and 17, which do not generally include flame holders, are also put into action, in accordance with the method described in U.S. Patent No. 3,102,392 of June 17, 1963.

Pre-heating of the by-pass flow enables a long path to be provided for the re-heated mixed flow, without any substantial increase in over-all length.

The drawing illustrates diagrammatically a device producing the desired result.

A regulator or governor R1 receives three input signals: a signal a from the pilots throttle M, a signal 6' from a total temperature detector in the primary or inner stream near the plane of confluence, and a signal 0 from a total temperature detector in the secondary or outer stream also near the plane of confluence. The regulator R1 is designed so as to keep the temperature 6 always equal to 0 by distributing fuel discharge from pump P, with adequate flows, first to the preheat manifold 12 then to the manifold 13. The lowering of the temperature due to the back-flow injection of cool fuel from this manifold, is compensated by the combustion of fuel discharge by the manifold 16 (which has no flame-holder), the injection pressure difference AP between the manifolds 13 and 16 being kept substantially constant.

After-burning beyond the confluence is controlled by a further regulator or governor R2 which receives, as the preceding one, the input signal 0: of the position of the pilots throttle M. This regulator determines the fuel injection pressures in the manifolds 14, 15 and 17, a difierential pressure AP being also maintained between the manifolds 14 and 17.

The regulator R1 and R2 control, besides the various fuel flows, the area of the nozzle 11 by controlling the oil pressures in the conventional jacks actuating the nozzle area adjusting members. This further parameter allows obtaining more easily the conditions required for operation at all loads.

It will be obvious that the invention is not limited to the embodiment particularly described, but that it also covers modifications thereof which can be obtained, within the scope of the appended claims, by using equivalent technical means; in particular, the annular combustion chamber 6 may be replaced by a chamber having separate flame tubes or by a mixed chamber (such as is referred to in the art as cannular).

What is claimed is:

l. A by-pass turbojet comprising a turbine to deliver a primary stream of relatively hot gas, air compressing means to deliver a secondary stream of relatively cold air, a jet pipe having a mixing zone for the mixing therein of said primary and secondary streams delivered to said jet pipe by said turbine and said compressing means, a nozzle with which said jet pipe communicates for the discharge of mixed gases of said primary and secondary streams, a heating device adapted to heat said secondary stream and positioned upstream of said mixing zone, and temperature responsive means controlling said heating device to maintain the temperature of said secondary stream to substantially the same level as that of the primary stream delivered by said turbine.

2. A jet-engine according to claim 1, including a reheat device for mixed gases of said primary and secondary streams.

3. A jet-engine according to claim '2, wherein said re-heat device is located in said mixing zone.

4. A by-pass turbojet comprising a turbine gas exhaust duct, a compressed air by-pass duct meeting said gas exhaust duct at a plane of junction, a jet-pipe extending downstream of said plane and wherein the flows through said ducts are collected and mixed, pre-heat burners in said by-pass duct upstream of said plane, reheat burners in said jet pipe downstream of said plane, means for supplying fuel to said pre-heat burners, a regulator adapted to control said fuel supply means, and total temperature detectors positioned respectively within said ducts just upstream of said plane and adapted to generate thermometric signals, said regulator actuated responsive to the thermometric signals to control said fuel supply means to maintain the detector temperatures substantially equal.

References Cited by the Examiner UNITED STATES PATENTS 2,955,414- 10/60 Hausmann 6035.6 3,054,254 9/62 Hopper 6035.6

MARK NEWMAN, Primary Examiner.

SAMUEL LEVINE, Examiner. 

1. A BY-PASS TURBOJECT COMPRISING A TURBINE TO DELIVER A PRIMARY STREAM OF RELATIVELY HOT GAS, AIR COMPRESSING MEANS TO DELIVER A SECONDARY STREAM OF RELATIVELY COLD AIR, A JET PIPE HAVING A MIXING ZONE FOR THE MIXING THEREIN OF SAID PRIMARY AND SECONDARY STREAMS DELIVERED TO SAID JET PIPE BY SAID TURBINE AND SAID COMPRESSING MEANS, A NOZZLE WITH WHICH SAID JET PIPE COMMUNICATES FOR THE DISCHARGE FOR MIXED GASES OF SAID PRIMARY AND SECONDARY 